I have a 2000 Pontiac Grand AM GT.108K miles. The car has been doing this thing every now and then when decelerating from highway speeds, the throttle will not come down. I have to fight the car with the brakes so that it doesn't lunge forward and hit the guy ahead of me. The only way to stop it is to put the car in park. When that happens, the RPM'S shoot up to 3000, 4000, etc. Before I pull the key out. When I go to start up again, the RPMS will immediately rev up to 3000 RPM, and then after 5 seconds or so settle in the normal idle range. My mechanic friend thinks it's the TPS, but no " check engine" light has come on. I've had it to two mechanics that have told me nothing is wrong with it. Help!
The TPS measures the angle of the throttle plate opening, it cannot (by itself) cause a high idle. Even if it were defective and read WOT when the throttle plate was closed, it would simply command the PCM to add more fuel and timing, this would cause it to stumble and run rich.
It sounds like the throttle plate or linkage are binding, or the throttle plate return spring is broke.
Other causes of a high idle would be a vacumm leak, but they usually do not repair themselves.
March, 13, 2007 AT 1:56 PM
Ahhh. Okay. You know, like many Grand Am owners I've had to have the intake manifold gasket replaced due to that Dex-cool issue. Do you think the new gasket (now about 2 years old) could be degrading again? That would cause a vacuum issue. Thanks again.
March, 13, 2007 AT 2:12 PM
Yes, could also cause coolant in the oil. GM is currently battling a class action suit over DEX-COOL as well as the manifold gasket. The issue with the manifold gasket was it is alleged that the replacements were defective.